Vulcanization of butyl rubber by 2, 6-di(acyloxymethyl)-4-hydrocarbylphenyl acylates



States VUL QANTZATIGN F BU'IYL RUBBER BY 2,6-Dl- (A CYL'0XYMETHYD-4-HYDROCARBYL PHENYL ACYLATES Pliny =9. Tawney, Passaic, N. J., assignor to United States Rubber Company, New York, N. Y., a corporation of New lersey No Drawing. Application September 27, 1955 Serial No. 537,045

4 Claims. (Cl. 260-853) RCOOCH-r- CHzOCOR wherein R is a hydrocarbon radical (e. g., an alkyl, aryl, aralkyl or cycloalkyl radical) and R is an alkyl radical, preferably a lower alkyl radical containing 8 carbon atoms or less, and (B) a heavy metal halide. The resulting vulcanizates have remarkable resistance to oxidation and to exposure to elevated temperatures, and they have other desirable physical properties. It was surprising to find that the stated organic compounds, in the presence of heavy metal halides, will produce such improved Butyl rubber vulcanizates, because the described organic compounds will not vulcanize Butyl rubber in the absence of the heavy metal halide.

Butyl rubber, or GR-l, is a generic name for any of the well known synthetic rubbery copolymers of an isoolefin with a minor amount of a conjugated diolefin. The isoolefins used generally have from 4 to 7 carbon atoms, and such isomonoolefins as isobutylene and 2- methyl-Z-butene are preferred. The diolefins used have from 4 to 8 carbon atoms. lsoprene and butadiene are the most important of these diolefins; others are piperylene; 2,3-dimethylbutadiene; 3-methyl-l,3-pentadiene; 2- methyl-l,3-pentadiene; 1,3-heXadiene and 2,4-henadiene. The Butyl rubber typically contains from about 0.5 to and seldom more than 10%, of copolymerized' diolefin on the total weight of the elastomer. This relatively small amount of unsaturation renders the behavior of Butyl rubber toward vulcanizing agents fundamentally different from the behavior of the more highly unsaturated rubbers, such as natural rubber or 63-8, and therefore experience with such highly unsaturated rubbers affords no basis for predicting the behavior of Butyl rubber toward a given vulcanizing agent.

Typical specific compounds of the above formula employed in the invention are 2,6-(acetoxymethyl)-4-methylphenyl acetate; 2,6-di(acetoxymethyl)-4-ethylphenyl acetate; 2,6-di(acetoxymethyl)-4-isopropylphenyl acetate; 2,6-di(acetoxymethyl)-4-tert-butylphenyl acetate; 2,6-di (acetoxymethyl)-4-tert,tert-octylphenyl acetate; 2,6-di (acetoxymethyl)-4-dodecylphenyl acetate; 2,6-di(acetoxy- -methyl)-4-phenylphenyl acetate; 2,6-di(acetoxymethyl)-4 benzylphenyl acetate; 2,6-di(acetoxymethyl)-4-cyclohexylphenyl acetate; 2,6-di(propionoxymethyl)-4-tert-butylatent 2,825,720 Patented Mar. 4,1958

lei pheuyl propionate; 2,6-di(butyroxymethyl)-4-tert-butylphenyl butyrate; 2,6-di(isobutyroxymethyl)-4-tert-butylphenyl isobutyrate; and 2,6-di(capryloxymethyl)-4-tertbutylphenyl coprylate.

The amount of the organic vulcanizing agent of the stated formula employed in the invention usually ranges from about 2 parts (by weight) to about 12 parts per 108 parts of the Butyl rubber. In general, a preferred range of the organic curing agent is from about4 parts to 8 parts per 100 of the rubber.

The heavy metal halide which may be regarded as a kind of catalyst or activator or curing supplement, since the organic compound itself will not cure the Butyl rubher-is usually used in amount of at least 0.5 part, and 1 preferably use about 1 to 3 parts, per 100 parts of the Butyl rubber. Although in some cases even larger amounts of the metal halide can be used, say lo'parts, it is not generally necessary or desirable to use'appreciably more than about 5 parts. In the majority of cases I lirnit the heavy metal halide to 5 parts or less, and I may even limit it to l or 2 parts at times. I customarily use a large amount of the heavy metal halide, e. g., from 5 to 10 parts, when i wish to cure the Butyl very rapidly at a low temperature, e. g., 100 C.

The heavy metal halides employed are exemplified by such known stable acidic halides as tin chloride, zinc chloride, iron chloride, and, in general, halides of the various metals usually classified as heavy metals (cf. the

periodic chart of the elements in Introductory College Chemistry by H. G. Deming, published by John Wiley and Sons, Inc). This class includes, inter alia, chromium chloride and nickel chloride, as well as cobalt chloride, manganese chloride and copper chloride. Although the copper halides may be used, I prefer not to use them because of the possible deleterious effect of the copper on the Butyl rubber. The heavy metal chlorides constitute the preferred class of activators or vulcanization adjuvants, although the heavy metal salts of other halides including bromine, fluorine, and iodine (such as stannic iodide) may also be used. Of the heavy metal chlorides, the most preferred are those of tin, iron and zinc. The heavy metal halides are efiective independently of the state of oxidation of the metal, and they are even oncetive if the halide is partially hydrolyzed, or is only a partial halide, as in zinc oxychloride.

In carrying out the invention, the Butyl rubber, the organic vulcanizing agent, and heavy metal halide, and any additional desired ingredients, may be mixed together in any desired order according to the procedures ordinarily used in mixing rubber compounds, with the aid of the usual rubber mixing equipment, such as an internal mixer or roll mill.

The vulcanizable mixture resulting from the foregoing ingredients may be fabricated into the desired form by the usual methods, such as calendering, extrusion, or molding, and subsequently vulcanized by heating, preferably while confined under pressure.

Preferably carbon black is present in the products made by the process of this invention. As is well known, carbon black greatly improves the tensile strength, abrasion resistance and other properties of sulfur-cured Butyl rubber as compared to the respective properties of similarly cured gum Butyl rubber. This improvement like- Wise is conferred by carbon black on Butyl rubber which is cured by the method of this invention. However, for certain products this improved tensile strength; etc., is not needed. Therefore, in its broadest aspect this invention relates to the cure of gum Butyl rubber and to Butyl'rubber and to Butyl rubber which contains other fillers, e. g., clays, titanium dioxide, etc., as well as to black-filled Butyl rubber.

The cure is conveniently carried out at temperatures aeaarao 200 to 205 C., provided that such high temperatures are not maintained long enough to cause thermal injury to the article. The time and temperature chosen for a particular cure not only are related inversely to each other but also are dependent on the amount of catalyst used. Therefore, the time and temperature of cure can be given only in the broad ranges shown above. Any skilled rubber compounder can easily determine conventionally the proper curing conditions for any particular stock.

The process of this invention is useful in making cured Butyl rubber products which resist aging at high temperatures in steam and/or air extremely well. Typical products are curing bags, steam hose, gaskets for equipment which must remain at high temperatures continuously or intermittently for long periods of time, belts,

4 the vulcanizing agents employed in the invention may be prepared by the foregoing procedure, starting with appropriate corresponding known materials.

The following example illustrates this invention. All parts are by weight.

Example A masterbatch was mixed on a rubber mill in the proportion of 100 parts of GR-I 15 (a copolymer of isobutylene: isoprene, 98:2, according to Rubber Age, 74, 561 (1954)), 50 parts of carbon black, 2 parts of stearic acid and parts of Indopol H300 (a commercially available polybutene sold as a plasticizer for rubbers). Stannous chloride dihydrate and 2,6-di(acetoxymethyl)-4-tert-butylphenyl acetate were then mixed with individual portions of the masterbatch on the mill to form a series of stocks which differed among themselves only in the amount of the curing agent. Portions of these stocks were cured in 6" x 6" x 0.1 molds under pressure at 161 C. (322 F.) for the individual times shown. The stocks then were tested conventionally, as shown, to determine the extent of cure and resistance to aging.

Stock 1 2 3 4 5 Masterbatch 157 157 157 157 157 811012, 215120 1. 1.8 1. 1.8 1.8 2,6-Di(acetoxymethyl)-4-tert-butyl-phenyl acetarp 2 4 6 8 12 Green Tests: Cure (min.)

15 7 222 1a; 1228 210 6 0 1, Tensfle Strength 850 1, 540 1, 460 1, 480 1, 460 120 1, 420 1, 470 1, 430 1, 340 l, 400 15 288 lit tit Elongation (p 23 8 388 220 280 230 120 390 210 150 160 160 15 08 88 538 30 210 1 18 1 100 percent Modulus (p. s. 1.). 60 130 230 380 310 390 190 430 700 570 610 Aging Tests (60-minute cures):

Tensile Strengths (p. s. i.)

green 850 1. 540 1. 460 1, 480 1, 460 aged 3 days in steam 1,140 1, 160 1,050 1,070 1, aged 24 hrs. in air 1, 070 1, 350 1, 260 1, 260 1, aged 48 hrs. in air 830 1, 180 1, 330 1, 090 1,060 Elongation (percent)- green 680 400 220 280 230 aged 3 days in steam 350 190 130 120 aged 24 hrs. in alr 350 190 120 110 70, aged 48 hrs. in air 380 230 140 100 90 100 percent Modulus (p. s. i.)-

130 230 380 310 390 200 370 640 510 660 190 410 790 1, 000 aged 48 hrs. in air 410 740 900 B All steam aging tests were made at 164 C.

(85 p. s. i. of steam.)

inner tubes, tires, motor mountin s, flexible hot air ducts, hot water bottles, etc. The cured products may also be kept in contact with copper or silver articles, which would be tarnished by Butyl rubber products cured by, or containing, sulfur.

The vulcanizing agents used in this invention are easily made by esterifying an appropriate 2,6-dimethylol-4- hydrocarbylphenol with the anhydride of the appropriate fatty acid. This method is described in detail by Barthel, I. prakt. Chem. 161, 77-80 (1942), and used by him to make one of the said vulcanizing agents-2,6-di(acetoxymethyl)-4-methylphenyl acetate. This ester is distillable in vacuo, but in general the esters used in this invention are distillable only with difficulty. Thus, 2,6- di(acetoxymethyl)-4-tert-butylpheny1 acetate is a viscous, almost colorless oil obtained as a residue from evaporation, in high vacuo, of the excess acetic anhydride and the acetic acid formed in the esterification. The physical properties of the residue agree with those calculated for (3 11- 0 It will be understood that any and all of This example shows that 2,6-di(acetoxymethyl)-4-tertbutylphenyl acetate is a good curing agent for Butyl rubber, and that the cured stocks age extremely Well.

Having thus described my invention, what I claim and desire to protect by Letters Patent is:

1. A method of vulcanizing a synthetic rubbery copolymer of an isoolefin having from 4 to 7 carbon atoms with from 0.5 to 10% of a conjugated diolefin having from 4 to 8 carbon atoms, comprising heating 100parts by weight of the said rubber at a temperature of from 100 C. to 205 C. for from 5 minutes to 3 hours, in admixture with from 2 to 12 parts of (A) a compound of the formula OCOR' RCOOCH CHrOCOR' wherein R is a radical selected from the group consisting of alkyl, aryl, aralkyl and cycloalkyl radical and R is a lower alkyl radical, and (B) from 0.5 to 10 parts of a heavy metal halide.

2. A method of vulcanizing a synthetic rubbery copolymer of isobutylene with from 0.5 to 10% of isoprene comprising heating 100 parts by weight of said rubber at a temperature of from 150 C. to 205 C. for from 5 minutes to 3 hours, in admixture with from 4 to 8 parts of 2,6-di(acetoxymethyl)-4-tert-butylphenyl acetate and from 1 to 5 parts of a heavy metal chloride.

3. An improved vulcanizate characterized by resistance to deterioration at elevated temperatures comprising 100 parts by Weight of a synthetic rubbery copolymer of an isoolefin having from 4 to 7 carbon atoms with from 0.5 to 10% of a conjugated diolefin having from 4 to 8 carbon atoms, vulcanized with from 2 to 12 parts of (A) a compound of the formula B'COOCHg- CHgOCOB' 6 wherein R is a radical selected from the group consisting of alkyl, aryl, aralkyl and cycloalkyl radical and R is a lower alkyl radical, and (B) from 0.5 to 10 parts of a heavy metal halide.

4. An improved vulcanizate characterized by resistance to oxidation at elevated temperatures comprising 106 parts by weight of a synthetic rubbery copolymer of isobutylene with from 0.5 to 10% of isoprene, vulcanized with from 4 to 8 parts of 2,6-di(acetoxymethyl)-4-tertbutylphenol acetate and from 1 to 5 parts of a heavy metal chloride.

OTHER REFERENCES Van der Meer: Rubber Chem. Tech. 18, 853-873 (1945).

UNITED STATES PATENT oTTTeT QERTll lQAlE GT QQRRECTWN Patent No, 2 825 72O March 4 1958 Pliny On Tawney It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected belowo Column 1 lines 23 to 30 column 41 lines 69 to 75 and column 5 lines 19 t0 .25 the structural formula each occurrence should appear as shown below instead of as in the patent:

GCOR

. J i RCOOCH v CH OCOR Signed and sealed this 22nd day of September 1964c (SEAL) Attest:

ERNEST W, SWIDER EDWARD Jo BRENNER Attesting "Officer Commissioner of Patents 

1. A METHOD OF VULCANIZING SYNTHETIC RUBBER COPOLYMER OF AN ISOOLEFIN HAVING FROM 4 TO 7 CARBON ATOMS WITH FROM 0.5 TO 10% OF A CONJUGATED DIOLEFIN HAVING FROM 4 TO 8 CARBON ATOMS, COMPRISING HEATING 100 PARTS BY WEIGHT OF THE SAID RUBBER AT A TEMPERATURE OF FROM 100*C. TO 205*C FOR FROM 5 MINUTES TO 3 HOURS, IN ADMIXTURE WITH FROM 3 TO 12 PARTS OF (A) A COMPOUND OF THE FORMULA 